Expandable Bolt With Thrust Element

ABSTRACT

The present invention includes a rock bolt having a longitudinally expandable tube. The tube includes a longitudinally extending depression that defines a temporary enclosed longitudinal passageway. The rock bolt further includes a shielded distal end to prevent debris from entering the temporary enclosed longitudinal passageway. The distal end includes a thrust element that facilitates movement of loose material across the rock bolt as it is advanced in a borehole. The present invention also includes a method of making such a rock bolt and a method of using such a rock bolt.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a rock bolt having an expandable tube and a shielded distal end bearing a thrust element, a method of making such a rock bolt, and a method of using such a rock bolt.

2. Description of Related Art

Rock bolts are used in underground mines, such as coal mines, to support the roof and ribs. Installation of conventional rock bolts involves drilling a borehole into the rock to a desired depth using an elongated drilling tool (termed the “drill steel”), removing the drill steel from the borehole, optionally inserting adhesive resin cartridges, and retaining the cartridges in the blind end of the borehole while a bolt, optionally bearing an expansion anchor, is installed into the borehole. The free end of the bolt extending out of the borehole is received by a chuck of a bolting machine. The bolting machine rotates the bolt within the borehole to mix the adhesive resin and/or expand the expansion anchor.

Other rock bolts comprise a longitudinally expandable tube that includes a longitudinally extending depression between two curved outer portions where the tube is partially collapsed on itself. The ends of the tube are folded over to create two enclosed cavities in the curved outer portions of the tube while a temporary passageway defined by the depression remains open on the ends. After placing the rock bolt in the pre-drilled borehole, pressurized fluid is delivered into the two cavities to force the depression outward, expand the tube, and compress it against the surrounding rock. Until the expansion has been completed, the ends of the passageway defined by the depression are open so that debris from the borehole can fall into the passageway defined by the depression.

SUMMARY OF THE INVENTION

The present invention includes a rock bolt having a longitudinally expandable tube. The tube includes a longitudinally extending depression that defines a temporary, enclosed longitudinal passageway. A thrust element is positioned at a distal end of the rock bolt and may be arranged in use to deflect loose material disposed in the bore as the rock bolt is inserted, thus facilitating movement of the material past the rock bolt when installed in a borehole.

The thrust element may assist insertion of the rock bolt in the bore and/or may inhibit compaction of that material in the blind end of the bore. Compaction of loose material in the bore is problematic as it reduces the effective length of the bore and may prevent the rock bolt from being fully inserted into bore unless that borehole is of extended length.

The thrust element may form part of a cover of the rock bolt to prevent debris from entering the temporary, enclosed longitudinal passageway, ease insertion of the rock bolt into the borehole, and assist in alignment of the rock bolt in the borehole. Alternatively the thrust element may form an extension of that cover and be fixed to the cover. The cover may be a plug or a cap and may provide a rounded tip for the rock bolt. The plug may be spherical. The cap may be attached such that its proximal end abuts the distal end of the rock bolt, is inserted into the distal end of the rock bolt, or extends beyond the distal end and along the sidewall of the rock bolt. In another form, the thrust element may be fixed directly to the rock bolt.

In one form, the thrust element is fixed in place by welding, but may be fixed by other means such as crimping, or through a coupling (such as a threaded coupling arrangement) or by adhesive bonding. In a particular form, the connection is only loaded in compression as the rock bolt is driven into the bore without requiring rotation. In one form, this drive action is by a percussive force.

The thrust element may take various forms but in general includes a profiling that promotes radial deflection of the material as the rock bolt is inserted axially into the bore. In one form, the thrust element may be conical or frustoconical having a wall surface that extends from an apex of the element to an engagement end where the element is mounted to the rock bolt. The surface of the thrust element extending between the apex and the engagement end may be faceted.

In another form, the thrust element may be more akin to a drill bit and may include channels or flutes that allow for radial flow of material as the rock bolt is inserted into the bore.

The present invention also includes a method of manufacturing a rock bolt, including providing an expandable member including an expandable tube and an end fitting where the expandable tube has a longitudinally extending depression disposed between a pair of outer portions of the tube, the exterior of the tube defines a temporary, enclosed longitudinal passageway having an open distal end, and the outer portions of the tube have closed distal ends, and enclosing the expandable member with a cover such that a distal open end of the temporary, enclosed longitudinal passageway of the expandable tube is covered. The cover may be a plug or a cap and may provide a rounded tip for the rock bolt. The cover may also include a thrust element arranged in use to deflect loose material disposed in the bore as the rock bolt is inserted, thus facilitating movement of material past the bolt when installed in a borehole. The method may also include placing a stiffening tube on a proximal end of the expandable tube such that the stiffening tube surrounds the proximal end of the expandable tube and has an opening that aligns with a corresponding opening in the expandable tube, thereby providing fluid communication to an interior of the expandable tube.

The present invention further includes a method of using a rock bolt, including providing a rock bolt having an expandable member including an expandable tube having a temporary, enclosed longitudinal passageway with an open distal end, and a cover at a distal end of the rock bolt covering the temporary longitudinal passageway; drilling a borehole in rock; placing the rock bolt in the borehole; expanding the tube by providing pressurized fluid to the interior of the tube, thereby providing frictional engagement between an exterior of the tube and an interior of the borehole; and draining the fluid from the interior of the tube. The cover may be a plug or a cap and may provide a rounded tip for the rock bolt.

The present invention further includes a method of using a rock bolt including providing a rock bolt having an expandable member including an expandable tube having a temporary enclosed longitudinal passageway with an open distal end, and a thrust element at the distal end; drilling a borehole in rock; inserting the rock bolt in the borehole whereby loose material in the bore is deflected by the thrust element; expanding the tube by providing pressurized fluid to the interior of the tube, thereby providing frictional engagement between an exterior of the tube and an interior of the tube thereby providing frictional engagement between an exterior of the tube and an interior of the borehole; and draining fluid from the interior of the tube. The thrust element may generally include a profiling that promotes radial deflection of the material as the rock bolt is inserted axially into the bore. The thrust element may comprise a cover for the distal end or may form an extension of that cover.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a rock bolt produced according to the present invention;

FIG. 2 is a cross-section taken along lines 1-1 of FIG. 1;

FIG. 3 is a cross-section taken along lines 2-2 of FIG. 1, as installed in rock strata;

FIG. 4 is a longitudinal cross-section of the distal end of a rock bolt according to one embodiment of the present invention;

FIG. 5 is a longitudinal cross-section of the distal end of a rock bolt according to a second embodiment of the present invention;

FIG. 6 is a longitudinal cross-section of the distal end of a rock bolt according to a third embodiment of the present invention;

FIG. 7 is a longitudinal cross-section of the distal end of a rock bolt according to a fourth embodiment of the present invention;

FIG. 8 is a side view of a distal end of rock bolt according to a fifth embodiment of the present invention;

FIG. 9 is a longitudinal cross-section of the distal end of a rock bolt according to FIG. 8;

FIG. 10 is a side view of a thrust element for use in the rock bolt of FIG. 8;

FIG. 11 is a perspective view of a thrust element for use in the rock bolt of FIG. 8;

FIG. 12 is a longitudinal cross-section of the distal end of a rock bolt according to a sixth embodiment of the present invention;

FIG. 13 is a perspective view of a thrust element for use in the rock bolt of FIG. 12;

FIG. 14 is a side view of a thrust element for use in the rock bolt of FIG. 12;

FIG. 15 is a longitudinal cross-section of the distal end of a rock bolt according to a seventh embodiment of the present invention;

FIG. 16 is a perspective view of a thrust element for use in the rock bolt of FIG. 15;

FIG. 17 is a side view of a thrust element for use in the rock bolt of FIG. 15;

FIG. 18 is a longitudinal cross-section of the distal end of a rock bolt according to an eighth embodiment of the present invention;

FIG. 19 is a perspective view of a thrust element for use in the rock bolt of FIG. 18; and

FIG. 20 is a side view of a thrust element for use in the rock bolt of FIG. 18.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawing figures in which like reference numbers refer to like elements, FIG. 1 shows a rock bolt 2 which includes an expandable tube 4 having an initial cross-sectional profile as shown in FIG. 2. The tube 4 is partially collapsed upon itself (such as by rolling or drawing) so as to provide a depressed region 6 between two curved outer portions 8, 10 extending longitudinally along the tube 4. The tube 4 is produced from a steel alloy or the like having sufficient strength to function in rock support, even after deformation from internal hydraulic pressure as described below. A first stiffening tube 14, having a sidewall and two open ends, is attached to and surrounds a proximal end 15 of the tube 4. A lip 18 may extend from stiffening tube 14 for engaging with a rock surface when the rock bolt 2 is inserted in the borehole.

A second stiffening tube 20, having a sidewall and two open ends, is attached to and surrounds a distal end 21 of tube 4 leaving the end of the tube 4 uncovered. A cover 22 covers the opening in a distal end 23 of second stiffening tube 20, the tube 4, or both and may be fixed thereto by welding or the like. The outer curved portions 8, 10 of tube 4 abut one another to define a temporary main passageway 26 as well as interior passageways 28, 30. Main passageway 26 is open at the distal end 21 of tube 4 while interior passageways 28, 30 are closed as shown in FIGS. 4-7. As shown in FIG. 1, the first stiffening tube 14 defines an opening 34 which is aligned with an opening (not shown) in tube 4, such that the openings are in fluid communication with interior passageways 28, 30.

In operation, a borehole is drilled into the rock to the desired depth and the bolt 2 is inserted through a bearing plate and into the borehole. A source of pressurized fluid, such as water, is delivered through the opening 34 of the first stiffening tube 14 and an opening in tube 4 into interior passageways 28, 30. When passageways 28, 30 are filled, the further addition of fluid creates sufficient hydraulic pressure to force open the tube 4, such that passageways 28, 30 are conjoined as an interior 35 of the tube 4 expanding the tube 4, and ultimately compressing the tube 4 against the surrounding rock of the borehole. See FIG. 3. As a result, main passageway 26 no longer exists. When the tube 4 is fully expanded and no further fluid is received therein, the fluid supply is removed and the fluid is drained. In this manner, the expanded tube 4 frictionally anchors into and/or against the surrounding rock R.

The cover 22 may take the form of a plug or a cap. In one embodiment, the cover 22 is a plug 122 or a plug 222, as shown in FIGS. 4 and 5, respectively. The plug 122, 222 is placed in the opening in the distal end 23 of tube 20 such that a first portion 124, 224 thereof is exposed and a second portion 125, 225 is in the interior of the tube 20. The plug 122, 222 may take any suitable shape (such as rounded) as long as the main passageway 26 is covered. The plug 122, 222 may be made of steel or any other suitable material. The plug 122, 222 may be fixed to the rock bolt 102, 202 by welding or the like. For example, tack welds 32, spaced apart around the circumference of the plug 122, 222 may be used to attach the plug 122, 222 to tube 20.

In one embodiment, such as for rock bolt 102, shown in FIG. 4, plug 122 is spherical. Plug 122 may be placed such that the first exposed portion 124 is one hemisphere of spherical plug 122 and the second portion 125 inside the opening in the distal end 23 of second stiffening tube 20 is the other hemisphere as shown. Alternatively, the plug 122 may be placed such that less of plug 122 is exposed or more of plug 122 is exposed as long as the main passageway 26 is covered. Plug 122 may take the form of a polished or unpolished ball bearing.

In another embodiment, such as for rock bolt 202, shown in FIG. 5, the first exposed portion 224 of the plug 222 may be dome shaped and the second portion 225 extending into tube 20 may be cylindrical. The second cylindrical portion 225 may further have a beveled edge 227 as shown.

Alternatively, the cover 22 may be a cap 322 or a cap 422, as shown in FIGS. 6 and 7, respectively. Cap 322, 422 may take any suitable shape (such as rounded) as long as the main passageway 26 is covered. The cap 322, 422 may be made of steel or any other suitable material. Cap 322, 422 may be fixed to the rock bolt 302, 402 by welding or the like. For example, tack welds 32 spaced apart around the circumference of the proximal end 329, 429 of cap 322, 422 may be used to attach cap 322, 422 to respective tube 20.

In one embodiment, such as for rock bolt 302, shown in FIG. 6, cap 322 is hemispherical, and the open proximal end 329 of cap 322 abuts distal end 23 of tube 20. Cap 322 is shown to be hollow but it could also be solid (not shown), for example, a sphere, such as plug 122 in FIG. 4, cut in half.

In another embodiment, such as for rock bolt 402, shown in FIG. 7, cap 422 has a closed distal end 434, an open proximal end 429, and a sidewall 436 extending from the closed distal end 434 to the open proximal end 429 creating an inner cavity 438. Cap 422 is placed over tube 20 such that tube 20 and the distal end 21 of tube 4 are received in the inner cavity 438. The sidewall 436 of cap 422 extends along the sidewall of tube 20. Cap 422 can be fabricated using any suitable means including, but not limited to, stamping, molding, or attaching a cover portion to a cylindrical tube. The distal end 434 of cap 422 may be hollow (as shown) or may be solid (not shown) as described above for cap 322 of rock bolt 302.

In another embodiment (not shown), cap 422 could be sized such that its sidewall 436 fits inside the distal end 23 of tube 20 such that distal end 434 of cap 422 extends beyond distal end 23 of tube 20. A portion of sidewall 436 may extend beyond the distal end 23 of tube 20 or the length of the sidewall 436 may be adjusted so that only distal end 434 extends beyond distal end 23 of tube 20.

In further embodiments such as for inserting the rock bolt into risible ground or ground into which it is difficult to insert an expandable bolt, a thrust element (522, 622, 722, or 822) may be provided at the distal end 23 of the rock bolt as shown in FIGS. 8-20. The thrust element may comprise a cover for the distal end 23, or may be otherwise associated with the distal end 23, such as being directly connected to the distal end, or form an extension of the cover 22.

The thrust element may be arranged in use to deflect loose material disposed in the bore as the rock bolt is inserted. This may assist insertion of the rock bolt in the bore and/or may inhibit compaction of that material in the blind end of the bore. Compaction of loose material in the bore end is problematic as it reduces the effective length of the bore and may prevent the rock bolt from being fully inserted into a bore unless that borehole is of extended length. It is undesirable to extend the length of the borehole as this adds both time and expense to the strata support operation.

In the form illustrated in FIGS. 8-11, thrust element 522 is in the form of a cone and extends from an apex 540 to an engagement end 542. The tapered surface of the element 522 extending between the apex 540 and the engagement end 542 comprises a plurality of angled facets 544. These angled facets allow loose material within the bore to be deflected in a radial direction (relative to the axis of the bore). Such movement of the loose material may aid insertion of the rock bolt in the bore and may inhibit compaction of the loose material in the end of the bore.

In some forms the engagement end 542 comprises an engagement portion 525 adapted to be inserted into the distal end 23 of the stiffening tube 20. In the form illustrated in FIGS. 8-11, the engagement portion 525 is in the form of a hemisphere adapted to be inserted into the distal end 23. The engagement portion further includes a collar section 526 that bears against the interior of the distal end 23 and a downwardly facing engagement shoulder 527 that locates over the distal end 23, thereby providing a cover for the distal end 23. Further, as illustrated the thrust element 522 which is typically made from metal, is fixed to the distal end 23 by tack welds 32. It will be appreciated that the thrust element 522 may be fixed by other means such as by crimping, a coupling (such as a threaded coupling) or by adhesive bonding.

In the form illustrated in FIGS. 12-15, thrust element 622 is frustoconical and extends from a truncated apex 640 to an engagement end 642. The surface of the element 622 extending between the apex 640 and the engagement end 642 comprises a plurality of angled facets 644. Similar to the previous embodiment, these angled facets 644 allow loose material within the bore to be deflected in a radial direction (relative to the axis of the bore). Again, the thrust element 622 forms the cover for the distal end 23 and may be welded by tack welds 32 to the end 23 with the engagement end 642 comprising an engagement portion 625 and being adapted to be inserted into the distal end 23 of the stiffening tube 20. In the form illustrated in FIGS. 12 through 14, the engagement portion 625 includes a hemisphere adapted to be inserted into the distal end 23, a collar section 626 which bears against the interior of the of the distal end 23 and a downwardly-facing engagement shoulder that locates over the distal end 23.

In the form illustrated in FIGS. 15-17, thrust element 722 extends from a thrust end 740 to an engagement end 742. The element 722 is made akin to a drill bit and the thrust end 740 is in the form of a profiled head having opposing angled blade surfaces 746 spaced apart about an upper surface of the thrust end 740. A central depression 747 is positioned intermediate the angled blade surfaces 746. The engagement end comprises an engagement portion 725 which comprises an engagement shoulder 748 that bears against the distal end 23 and an engagement flange 749 that locates in facing relation with the interior of the distal end 23. In this way, the thrust element 722 also forms a cover for the distal end 23. Channels 750 extend longitudinally along the element 722 between the blades 746. These channels are arranged to allow loose material to flow past the thrust element 722 as the rock bolt is advanced along the bore during insertion thereby inhibiting compaction of material at the end of the bore. Again, in the illustrated form, the thrust element 722 is welded to the distal end 23 by tack welds 32.

In a further form illustrated in FIGS. 18-20, thrust element 822 extends from a thrust end 840 to an engagement end 842. The thrust end 840 is in the form of a profiled head having two protrusions 846 spaced apart about an upper surface of the thrust end 840. A domed surface 847 is positioned intermediate the protrusions 846. The engagement end 842 comprises an engagement shoulder 848 which locates over the distal end 23 and a threaded shaft 849. The shaft 849 locates within the distal end and is arranged to engage with a complementary interior thread 36 formed on the interior of the tube 20 to secure the element 822 to the end 23. The spacing between the protrusions 846 allows material flow across the element 822 on insertion of the rock bolt into a bore containing loose material.

The rock bolt can be made by providing an expandable member which includes an expandable tube 4 and an end fitting (stiffening tube 20) on the distal end 21 of the expandable tube 4. The expandable tube 4 has a longitudinally extending depression 6 disposed between a pair of curved outer portions of the tube 8, 10. The exterior of the tube defines a temporary, enclosed longitudinal passageway 26 having an open distal end 23 and the outer portions of the tube 4 define internal passageways 28, 30 which have closed distal ends 23. The distal end of the tube 4 is then enclosed with a cover 22 so as to cover the distal open end 23 of the temporary, enclosed longitudinal passageway 26. The cover 22 may be in the form of a plug 122, 222 or a cap 322, 422 and may be rounded. The cover 22 may be secured to the expandable tube 4 by welding or any other suitable method. The method may also include placing a stiffening tube 20 on a proximal end 15 of the expandable tube 4 such that the stiffening tube 20 surrounds the proximal end 15 of the expandable tube 4 and has an opening 34 that aligns with a corresponding opening in the expandable tube 4, thereby providing fluid communication to an interior of the expandable tube 4. The stiffening tube 20 may be attached to the expandable tube 4 by welding, crimping or any other suitable method.

The cover keeps debris from entering the main passageway of the rock bolt when the rock bolt is in the unexpanded condition. It also allows the rock bolt to be more easily inserted and centered in the borehole. The domed end of the rock bolt created by the cover eliminates the sharp angles at the distal end of the rock bolt which can tend to get caught on the sides of the borehole. The domed end also allows the rock bolt to be centered more easily in the borehole.

The cover also has the advantage of reduced manufacturing costs compared to other methods of rounding the end, for example, building up weld metal on top of a blank to round the end. The cover may be held in place with a minimal number of tack welds as described above simplifying fabrication and reducing costs. In addition, manufacturing becomes even easier when producing a rock bolt according to embodiment 102, shown in FIG. 4. The spherical plug 122 may be placed in tube 20 in any orientation simplifying assembly and, thus reducing assembly time.

In general use, the expandable rock bolt with thrust element is inserted into a pre-drilled borehole, without rotation thereof necessary, although in certain instances the expandable rock bolt with thrust element may be at least slightly rotated about its longitudinal axis. Such pre-drilled boreholes may at least partially refill with loose rock or the like. The thrust element deflects such loose material to ease the insertion of the bolt into the borehole, with the remainder of installation of the expandable rock bolt with thrust element being the same or similar to the expandable bolt with shielded tip as described above.

The thrust element positioned on the distal end of the expandable rock bolt reduces the difficulty of inserting the expandable rock bolt into a bore made in risible or gravelly earth. In these circumstances the material tends to move past or be deflected by the element into the wall of the bore. The thrust element allows the bolts to be more easily inserted by compacting the loose material against the wall of the bore or moving loose earth material away from the advancing front of the rock bolt as it is being inserted in the bore. This allows the expandable bolt to be inserted into the bore without the risk that there will be a build up of material in the end of the bore that would prevent the rock bolt from being fully inserted. The use of a thrust element on the rock bolt is particularly useful when a percussive force is applied to drive the rock bolt in place and typically does not require any rotation to be applied to the bolt.

The foregoing description sets forth the preferred embodiments of the invention at the present time. Various modifications, additions, and alternative designs will, of course, become apparent to those skilled in the art in light of the foregoing teachings without departing from the scope of the invention. The scope of the invention is indicated by the following claims rather than by the foregoing description. All changes and variations that fall within the meaning and range of equivalency of the claims are to be embraced within their scope. Specifically, while embodiments herein have been described as having a rounded cover, covers having any shape that covers the main passageway of the rock bolt are considered within the scope of the invention. 

The invention claimed is:
 1. A rock bolt comprising: an expandable tube having a longitudinally extending depression disposed between a pair of outer portions of the tube, wherein the exterior of the tube defines a temporary, enclosed longitudinal passageway; and a thrust element positioned at a distal end of the rock bolt to facilitate movement of material past the rock bolt when installed in a borehole.
 2. The rock bolt according to claim 1, wherein the thrust element includes a plurality of projections and at least one channel between the projections that facilitates material flow across the rock bolt as it is advanced in a borehole.
 3. The rock bolt according to claim 1, wherein the thrust element is tapered from a thrust end to an engagement end.
 4. The rock bolt according to claim 1 wherein the thrust element includes a plurality of facets extending between the thrust end and the engagement end.
 5. The rock bolt according to claim 1, further comprising a cover covering the temporary longitudinal passageway, wherein the thrust element is adapted to engage with, or form part of the cover.
 6. The rock bolt according to claim 1, further comprising a stiffener tube surrounding the distal end of the expandable tube, wherein the thrust element is adapted to engage the stiffener tube.
 7. The rock bolt according to claim 6, wherein the thrust element comprises an engagement portion received within the stiffener tube.
 8. A method of using a rock bolt comprising: providing a rock bolt comprising an expandable tube having a temporary enclosed longitudinal passageway with an open distal end and an end fitting, and a thrust element at a distal end of the expandable tube covering the temporary longitudinal passageway; inserting the rock bolt in a borehole, whereby material in the borehole is deflected by the thrust element as it is advanced in the borehole; expanding the tube by providing pressurized fluid to the interior of the tube, thereby providing frictional engagement between an exterior of the tube and an interior of the borehole; and draining the fluid from the interior of the tube.
 9. The method according to claim 8, wherein the thrust element includes a plurality of projections and at least one channel between the projections.
 10. The method according to claim 8, wherein the thrust element is tapered from a thrust end to an engagement end.
 11. The method according to claim 8, wherein the thrust element includes a plurality of facets extending between the thrust end and the engagement end.
 12. The method according to claim 8, further comprising a cover covering the temporary longitudinal passageway, wherein the thrust element is adapted to engage with, or form part of, the cover.
 13. The method according to claim 8, further comprising a stiffener tube surrounding the distal end of the expandable tube, wherein the thrust element is adapted to engage the stiffener tube.
 14. The method according to claim 13, wherein the thrust element comprises an engagement portion received within the stiffener tube.
 15. The method according to claim 8, wherein the rock bolt is inserted into a borehole with a percussive force. 